Plague Hall of Fame:
Plague of Athens. 430-426BC. "Typhoid fever." Caused by bacteria (salmonella)
Kills a quarter of the population of Athens. Would have killed more if it was less virulent but ended up killing people at a faster rate than they could spread it.
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Antonine Plague. 165-180AD. Smallpox. Kills a quarter of those infected. At height, as many as 5,000 a day dying in Rome.
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First Plague Pandemic: 541-542 AD. "Plague of Justinian" (the Roman Emperor at the time, who also contracted it). Caused by bacteria, Yersinia pestis, carried by rats who were carried in ships. Flea bites rat, then flea bites human. Also extremely contagious human/human.
Kills half of all the people in the Roman Empire. 10,000 deaths a day in Constantinople (now Istanbul)
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Second Plague Pandemic: 1334-1352 AD. "Black Death". Also caused by Yersinia pestis (i.e. bacteriological). Originates in China but is eventually spread to Europe through trade (rat-infested ships) and then worldwide.
Kills half the people in Europe.
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Third Plague Pandemic: 1866-1960s. Also caused by, you guessed it, Yersinia pestis. Also originated in China & carried around the world in ships (rats & flea-infested cargo)
Kills 10 million people in India alone.
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Influenza pandemic. 1918-1920. "Spanish Flu." Virus, however death caused by bacteriological secondary infection (pneumonia).
Infects 500 million people (~ one third of the world's population (1.8 billion at the time)). Kills as many as 100 million.
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The discovery of antibiotics effectively put an end to Yersinia pestis, ending the "Black Death" type plagues and greatly reducing the consequences of secondary bacteriological infections in virus-caused diseases (i.e. the influenza pandemic of 1918).
Trivia: The first widely-known vaccination was a smallpox vaccination. Created by collecting scab material from those with smallpox, drying the scabs, and then grinding them into powder. Scab powder, containing dead smallpox virus, then inhaled into the nose.
Later refined into a real vaccine by Edward Jenner in 1796. Jenner collected pus from cows infected by cowpox and injected it into humans. Cowpox is similar enough genetically to smallpox that the immune system's learned reaction to cowpox is also effective against smallpox